Load handling hooks for cranes and hoists and the like are frequently equipped with gates and latches to prevent accidental disengagement of the load carrying sling, chain or such from the hook. Typically, such gates are movable from a position in relatively clearing relationship to the hook throat to a position bridging the throat. See U.S. Pat. No. 3,674,301 to Crook issued July 4, 1972 and No. 3,575,458 to Crook et al issued Apr. 20, 1971. Frequently such gates render the hook throat partially obstructed in the open position, sometimes posing a difficulty when loading the hook. It is desirable that the hook throat be as clear as possible for loading. The strength of such latches is usually relatively moderate as compared to the strength of the hook and a danger of failure exists should the load on the hook be accidentally transferred to the safety gate or latch. In general, the strength of a latching mechanism should be compatible with the strength of the hook to optimize the hook-latch combination capability consistent with safety considerations.
In various hook gates and closures of the prior art, the weight of a load on the hook acts against the latch mechanism itself, i.e., the greater the load, the more stress placed tending to open the latch mechanism which, if failure occurs, results in opening of the hook. See U.S. Pat. No. 2,864,644 to Marryatt issued Sept. 30, 1957. It is desirable that a load on the hook not exert a force on the latch mechanism in a direction toward opening the latch and, indeed, it is preferable that the hook closure be devised such that increased loading on the hook is accompanied by an increase in the force holding the closure assembly closed.
A further requirement of a latch or hook closure mechanism is that it does not promote fouling of the load sling or load chain as by having parts protruding from the hook proximate the intended position of the load sling on the hook on which elements of the load sling or chain could catch and hang. For example, see U.S. Pat. No. 2,027,376 to Grau issued Jan. 14, 1936. An added requirement of the closure mechanism is that it be rugged so as to be usable out of doors exposed to the elements.